Method of increasing the strength of a sprocket chain



Jan. 10, 1956 .1. J. BECK METHOD OF INCREASING THE STRENGTH OF A SPROCKET CHAIN Filed Nov. 24, 1950 2 Sheets-Sheet l FIGZ. F|G.l.

FIG.6. u

JOSEPH J. 550K INVENTOR.

BY 71 ,4, M

ATTORNEY Jan. 10, 1956 Filed Nov. 24, 1950 J. J. BECK 2,729,935

METHOD OF INCREASING THE STRENGTH OF A SPROCKET CHAIN 2 Sheets-Sheet 2 CLRVE c CURVE 0 I000 CIURVE B soc LOAD IN B /CURVE A 600 4o A',/ GAGE LEN TH-l3 PI'I'OHES 200 I60 .240 .320 .400 .480 CHAIN ELONGATION INCHES ATTORNEY United States Patent METHOD OF INCREASING THE STRENGTH OF A SPROCKET CHAIN Joseph J. Beck, Milwaukee, Wis., assignor to Chain Belt Company, Milwaukee, Wis., a corporation of Wiscousin This invention relates to improvement in the manufacture and construction of chain of the type having curled sections at the ends of the links, the links being connected by pins extending through the curled sections thereby forming a series of hinged joints. An example of such chain is shown in U. S. Patent No. 1,966,659 to Wynne et al., and the present invention will be describedin connection with chains of the type shown in the Wynne et al. patent.

It has heretofore been possible to produce chains of satisfactory strength for normal applications if the steel from which they are made is heat treated after forming to harden the links and to remove residual stresses created in the curled portions. When the chains are formed from what is commonly designated stainless steel of a type which it is not feasible to heat treat after forming, i. e., on account of its not responding to heat treatment, the yield strength is materially reduced because of the tendency of the curled portions to uncurl when a load is applied on the chain. This is partly caused by the ap plication of the load on the pitch line of the chain below the plane of the link, producing a moment tending to straighten out the curled portions. But the condition is exaggerated by the retention of stresses, due to the curling operation, which are nearly up to the yield point of the material. When such a chain is placed in tension, the stresses are cumulative resulting in yielding ofthe chain at a low work load.

The present invention provides a method whereby the links when formed and assembled will have residual stresses in the curled portions which will help to carry the load rather than add to the load, thereby increasing the working load capacity of the chain.

The invention has utility not only in connection with austenitio steels which are not readily hardened by heat treatment, but also when applied to other metals which respond to cold working, it provides. a procedure which may be used instead of heat treatment.

In the accompanying drawings, which illustrate one of the methods of practicing the invention and producing the improved chain:

Fig. 1 is an exploded, perspective view of two chain links of the type with which this invention is concerned; Fig. 2 illustrates a link of the type shown in Fig. l as it is held in a .die to over-curl the central knuckle at one end of the link;

Figs. 3, 4 and 5 illustrate successive changes in link contour as a result of the next forming operation;

, Fig. 6 is an enlarged side elevation of the curled portion illustrating the changes in contour as a result of the working operations; and

Fig. 7 is a graph showing the stress-strain relationship of links produced by the present method compared with those made in a conventional manner.

Referringto Fig. 1 of the drawings, eachof the links 11, which are formed from fiat plates of metal, has a central curled portion 12 at one end and spaced curled portions 13 at the other end. The curled portions 13 2,729,935 Patented Jan. 10,1956

are spaced apart a distance corresponding to the width of the central curl 12 and have cylindrical apertures of the same diameter as the aperture in the central curl so that a series of such links may be assembled end-to-end, with the holes in the overlapping, interfitted curled portions aligned. By inserting a connecting pin 13' through each set of aligned curled portions, an endless chain is formed having hinged, articulating joints. The knuckles ride in grooves in the sprockets, as illustrated in the Wynne et al. patent, and thus power can be transmitted to the chain to enable it to convey articles such as bottles, packages, etc. i

Experience has demonstrated that when a chain of the type described above is overloaded, the central curled portions 12 are the first to yield, and yielding manifests itself by the portion designated 18 lifting and tending to bend back on itself, which action will hereafter be referred to as uncurling. The result is an increase in the pitch, i. e., the distance between centers of the joints at the ends of each link, and such increase destroys proper action of the chain over the sprockets.

The present invention provides a method whereby residual compressive stresses instead of tension stresses are created inthe inside surface of the curled portion, which stresses resist the above described uncurling and greatly increase the yield strength.

From a practical standpoint, only the central curled portion 12 requires strengthening and the operations hereafter set forth will be described only in connection with that portion. Should it be necessary however to strengthen the curled portions 13, it will be appreciated that the same technique may be applied to do so.

In Fig. 2, the link formed in the conventional manner is placed in a fixed die member 14 which confines the spaced knuckles 13 and the flat central portion 15 of the link so that these portions are not affected by the forming operation illustrated in this figure. Relief is provided at 16 in the die 14 so that when the movable die 17 comes down on the back of the central curl 12, this portion of the link will be further curled or overcurled by shortening the pitch and increasing the distance from the center of the curl to the plane of the link.

The shape of the link after the above operation 'is illustrated in Fig. 3; the radius of curvature in the region designated 13 has been increased so that with the bottom portions 19 and 20 of the curled sections 12 and 13 respectively resting on horizontally aligned surfaces of the die 21, the flat portion 15 of the link slopes down wardly from the right to left as shown in said figure. The link is then brought to final shape by the die action illustrated in Fig. 4.

In Fig. 4, the movable die member 22 is illustrated engaging the flat central portion 15 of the link, while the opposite side of said portion as well as the two curled sections are resting on the die 21. The portion 18 of the curled section 12 is sprung upward just enough so that when the die 22 is retracted, as illustrated in Fig. 5, the correct final shape will result on account of springback of the metal.

The links are then assembled to make up the chain by inserting the pins 13 through the overlapping or interrect final shape. In either event, the pitch of the link at the end of the operation is less than the ultimate dethe. curled portions ..and,- then. pulling. these pins apart so that the-metal of .the linkisstretched beyond itselastic limit and beyond-the :final pitchrequired. -When the pressure is r'ele,ased, thefcurled or .eye portion 12 springs hack partially toapro duce the proper pitch. This" operatign.does'notaffeetthe. curled portion=13tor the reason heretofore. mentioned -that;:the portion 12 is the first to .yieldrunder conditions of overload.

Still another procedure is to assemble a strand of-links after theyuare eachshapedto formsirnilar to that shown in Fig. 3, and then to. grip the knuckles at the ends of the strandand pulltheentire strand -so .that the individual linksarestretched to.the correct pitch. Whilethereis some danger in the. latter procedure if the-links are nonuniform in ,physical characteristics that the individual links will be unevenly ..elongated,.if.the manufacture'of :theindividuallinks is. carefully performed, and uniform material isemployed, remarkable pitch accuracy is .obtained by this method, with resulting economy in manufacture.

:The eflect of the uncurling operation is illustrated in Fig. 6, wherein the full lines represent the position of the curled portion 12 of theilink. at the conclusion of the uncurling operation and the dotted lines the position and shape of, this portion priorto itsbeing uncurled. Residual-compressive stresseshavebeen imposed on'the inside'fibers ofthe curl at 23 and-residual tension stresses on theopposite outside fibers. The center of-the curl 12 has .now-beenmoved so as to form the correct pitch for the link.

.Inall threeprocedures, the stresses which are created are retained in the links when they are placed in service. Such residual stresses, i. e. stresses present when no load is applied, act in a compressive manner circumferentially onitheinside ofthe curled portion as a result of the-uncurling operation, instead of in a tensile manner, asthey formerly did.

TheIincrease in strength of thechain resulting from the present invention is-illustrated by-the graph shown in Fig. 7. In each test the ends of a strand of thirteen links of. chain werezheld in fixtures and the chains were pulled apartonia tensilettesting machine. Each curve represents an average of two or more tests. The load in pounds is plotted against elongation in inches.

.The chain test illustrated bycurve A involved a strand of standard 188 (18% chrome8% nickel) stainless steel chain .having one and one-half inch pitch-formed in the manner employed prior to the present invention. Atslightly over 200 pounds pull, A on the graph, elongationrdiscontinued being a straight line function of load, indicating the yield point of ,the chain.

The links used in the other tests,'hereafter described, were made frornthe same material, same gauge of metal, and in every respect were as similar as possible.

CurveB represents the stress-strain relationship of a strand of chain, the individual links of which wereformed bytollowing the operationdescribed in detail in the first part of thisdescription,usingthe dies illustrated in-Figs. 2-5. The yield point was increased trom 21-5 pounds'to 625ipounds, or roughly 300%.

Curve C shows an ultimate strength of -1035 pounds was obtained when the links were initially formedto the shapeillu stratedJay-Big. '3, but instead of being subsequently-formed jby dies asillus trated in' 4 and S, the ends werelgjripped and thenpulled away frorneach the .w.p sdqs ithas t q .cha le sth- Ihe 'ield..po int l) was obt p ed on curve after the a stea sf i ividu l vadsmit h 1 was stretched to increase the pitch of the links to the corperfect the .action L of I the chain over I the sprockets, the

teeth of which are designed in accordance with the pitch designation of the chain.

Th inva tic ghaxiu zbs describ -i li aclai 1. The methodof increasingtheyield strength of a sprocket chain link having a curled joint portion at one end of the link which comprises curling said portion so that the pitch of. the linkis v less than the ultimatedesired andtthen uncurling said.portion to increase the pitch to the desired .length, Qsaid lastrnentioned step imparting residual compressivetstresses,on-the inside surface-of-tlie curled portion. in the area -wherethe curled portion joins therest, ofsthe link. which are retained in thelink when displaced in service. a

2. .The method of increasing the-yield strength of a chain having an intermediate curledport-ion at one=end of eachzlink connected. in .-hinge fashion with spaced curled sections of an ladjoining link, which methodcomprises overcurlingz the.said intermediate .curled portions of each link .andithen uncurlingisaidvportions to bring the links to the correct: length and: impart residual compressivestresses on; the insideksurfacesnof said portions where they-join the rest of the link.

".3. :The.method lofproducing a chain link in a chain having jointslat each .end ofLthe link, oneend having a curled. portion for receiving .apin hingedlyconnecting-it withan adjoining: link which comprises-curling said end portionso that: the pitch of. the linkmeasured-by the distance betweenthecenterfioflhe, curled portion and the center of; the jointat theot-her end of the'linkisless'than the) ultimate :desiredgithen uncurling said end portion and allowing it 10. spring-back to increase the-pitch the required amount, .the .spring back from the uncurling operation setting uplresidual compressive stresses on the insideof the curled portion and increasing the yield strength of'the link,. and:.finally.assemblingLthe'link in the chain with. the compressive stresses still-retained inthecurled end portion.

.4. :The method of producing sprocket chain: having links with interconnected :hinged joints, each of said joints having a central curled. portion connected byta-pin with spaced, overlapping joint sections on an adjoining'link, whichrnethod comprises curlingthe; central curled portion ofl-eachrlinksothat the centerthereof is closer tlian that desired-to. the joint at the other end'of the link, and-then after connecting a plurality of such: links in a strand, pulling the .end'slof. the-strandapart. to bring the individual links after, springl-backto the correct length, thereby setting up residual compressive stresses on the'inside surfaces of the central curled'portions.

S. The method of producing a chainlink having a substantially flat central vportioirand curled end-portions; for connection with adjoining links, one-curled end portion forming the intermediate section of a hinge joint with; the curledrlsectionsl ofan adjoining link, which method comprises curling said intermediate end portion so that the pitch ofthe linktmeasured -by the distance between the centers of -the curled portions at each end of'the link is less than that desired and the center of the'interrnediate curled portion is further-fromthe plane of the flat central portion of the link than thecentei' of the curled-portion at the otherend of the link,, an'd then uncurling saidinterm diat nt e sethepit ther qi e m nda ie -t a. atw th i ded .P9I Q .l -R e ai tvlsa ath wav r n a m s n u resi ua compressive stresses on the inside of said intermediate curled portion and increasing the yield strength of the link.

6. The method of producing a chain link having a substantially fiat central section and curled end portions for connection with adjoining links, one curled end portion forming the intermediate section of a hinge joint with the curled sections of an adjoining link, which method comprises curling said intermediate end portion so that the center thereof is further from the plane of the flat central section than the centers of the curled portions at the other end of the link and then uncurling said intermediate end References Cited in the file of this patent UNITED STATES PATENTS Wynne July 17, 1934 Lauenstein Aug. 1, 1950 

